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10 February 2006

Sex Differences, Gender Differences in Brain s

No other topic is as likely to raise blood pressures and voices in academia, than the topic of sex differences in the brains of men and women. This newsrelease from the Society for Neuroscience, discusses a report on sex differences in the brains of mice. The research is published in the 1 Feb 2006 issue of the Journal of Neuroscience.

“We found unexpected differences in the white matter of male and female brains, which may have implications for the study of diseases that affect one gender more than the other, like multiple sclerosis,” says co-author and team leader Robert Skoff, PhD, of Wayne State University School of Medicine.

Myelin, a major component of the brain’s white matter, coats nerve cells and helps conduct messages through the central nervous system. The dramatic difference was “much greater than we anticipated,” the team noted.

Clarifying how sex differences in the brain are generated may provide critical insight into why disorders such as multiple sclerosis, autism, and depression have a much greater incidence in one gender over the other, says Christine Wagner, PhD, at the University at Albany, who has also reported on sex-based brain differences in rats.

Skoff’s team also discovered that the lifespan of myelin-forming cells is much shorter in female mice. Female mice produced up to twice the number of cells as males, and twice as many of these cells died in female brains. The greater turnover of cells in female brains may mean that myelin itself generates—and degenerates—at a greater rate in females, says Skoff. This finding could have implications for research on multiple sclerosis, a debilitating autoimmune disease characterized by myelin degeneration. About 400,000 Americans have multiple sclerosis, with two of three cases occurring in women.

Skoff’s team also showed that the composition of the brain’s white matter is regulated by hormones. Just like the female mice, castrated male mice showed greater turnover of myelin-forming cells. “These results show that hormones made outside the central nervous system, presumably testosterone, help regulate the number of myelin-forming cells and the amount of central nervous system myelin,” says Skoff. Recent studies show testosterone may have a protective effect in multiple sclerosis.

“The fact that sex hormones affect these cells and influence turnover rates extends our notions of how and where sex hormones act in the brain well beyond where most people are aware,” says Bruce McEwen, PhD, an expert on sex hormones at Rockefeller University.

Recent controversy over the Lawrence Summers Affair, has led some people to look into a possible neurobiological basis of sex differences, and caused other people to attempt to slam the lid on the entire issue.

A thorough look into the issue of sex differences and gender differences in brain function is likely to stir up much controversy. Even if excellent scientific research demonstrated valid, meaningful, and significant sex differences and gender differences in male and female brain function, in the current atomosphere of quasi-censorship it is unlikely that the research would be financed or duplicated.

The importance of understanding sex differences and gender difference is in being able to determine whether current social policy is warranted, or perhaps misguided in emphasis.